Rename `FamixTParametricEntity >> rootGenericEntity` as `genericEntity` about famix

[NicolasAnquetil]

May be I misunderstood the issue, but concretization can be a tree (even if it is rare):

If you have a generic with 2 type parameters (like Map<K,V>), then you can have a partial concretization where you specify only type (ex: MapStrings<V> extends MAP<String,V>), and then a complete concretization of this one.

[Gabriel-Darbord]

In the scenario you describe, there is an inheritance relationship between two concretizations:

A concretization tree always has a height of at most two, because an entity that is concrete can never also be generic in another concretization relation.
The following never happens:

There is always a single generic entity, and possibly several concrete entities:

The genericEntity method will always return the generic entity (the root) in a concretization relation.
This is what this method was intended to do, so this closes the issue.

Finding the root entity through multiple relations is more complicated, and most convenience methods don't take concretizations into account, see #718.